627 articles
All articles — Page 21
Every article in the chemistry library, newest first.
Electron Configuration Rules: Aufbau, Pauli and Hund Explained
The three rules that determine how electrons fill orbitals, the filling order and how to remember it, orbital box diagrams, noble-gas shorthand, and ions.
Stoichiometry Step by Step: The Mole Map Method
A beginner-friendly method for solving any stoichiometry problem — mass to mass, mass to moles, gases and solutions — built around one simple roadmap.
The Alkali Metals: Properties, Trends and Reactions of Group 1
Lithium, sodium, potassium, rubidium, cesium and francium: why they're so reactive, how their properties change down group 1, their reactions with water, and their everyday uses.
The 7 Diatomic Elements (and How to Remember Them)
The seven elements that exist as two-atom molecules — H₂, N₂, O₂, F₂, Cl₂, Br₂ and I₂ — why they pair up, the mnemonics that help you remember them, and why it matters in equations.
STP and Molar Volume: Why Is It 22.4 L (or 22.7 L)?
What standard temperature and pressure means, why textbooks give molar volumes of 22.4 L, 22.7 L and 24.5 L, and how to use molar volume in gas calculations.
Arrhenius, Brønsted-Lowry and Lewis Acids and Bases Explained
The three definitions of acids and bases, what each one adds, conjugate acid-base pairs, amphoteric substances, and how to tell which definition a question wants.
States of Matter: Solids, Liquids, Gases and Plasma
How particles behave in solids, liquids, gases and plasma, the names of every phase change, why temperature stays flat while things melt or boil, and which elements are solid, liquid or gas at room temperature.
The History of Atomic Models: From Dalton to Quantum Mechanics
How our picture of the atom evolved — Dalton's solid spheres, Thomson's plum pudding, Rutherford's nucleus, Bohr's orbits, Chadwick's neutron and the quantum mechanical model — and the experiments that changed each one.
How Carbon-14 Dating Works (and Its Limits)
How radiocarbon dating uses carbon-14's half-life to date once-living things, a worked example, why it only works back about 50,000 years, and why dates must be calibrated.
The Main Types of Chemical Reactions (With Examples)
Synthesis, decomposition, single and double displacement, combustion, neutralization and redox reactions — how to recognize each type, with balanced examples and a quick identification guide.
Polar vs. Nonpolar Molecules: How to Tell the Difference
How electronegativity makes bonds polar, why molecular shape decides whether a whole molecule is polar, a quick method with examples, and why polarity controls what dissolves in what.
The Atomic Radius Trend: Why Atoms Shrink Across a Period
Why atomic radius decreases across a period and increases down a group, how ionic radii compare, the lanthanide contraction, and how to rank atoms by size in exam questions.
How to Convert Grams to Moles (and Moles to Grams)
The one-step method for converting between grams and moles, worked examples for elements, compounds and hydrates, and the mistakes that cost students marks.
The Actinides: Uranium, Plutonium and the Radioactive f-Block
The 15 actinide elements from actinium to lawrencium: why they're all radioactive, which occur in nature, how the rest were made, and their roles in nuclear power, weapons, medicine and smoke detectors.
Why Is Gold Yellow? Relativity and the Colour of Metals
Almost every metal is silvery grey, but gold is yellow and copper is reddish. The explanation involves electrons moving at a significant fraction of the speed of light — here's how relativity colours gold.
Molarity vs. Molality: What's the Difference?
Molarity and molality compared: definitions, units, worked conversions, why molality ignores temperature, and when chemists use each one.
Boyle's, Charles's and Gay-Lussac's Laws: The Gas Laws Explained
The three classic gas laws, what each one means physically, the combined gas law, worked examples and the everyday situations where you can see them happen.
The pH Scale Explained: What pH Really Measures
What pH actually measures, why the scale is logarithmic, how pH and pOH relate, how to calculate pH, and the pH of everyday substances from lemon juice to bleach.
What Is an Ion? Cations, Anions and How Ions Form
What ions are, how atoms become cations and anions, how to predict an element's ion charge from the periodic table, and why ions matter in everything from salt to nerve signals.
The History of the Periodic Table: From Döbereiner to Mendeleev and Beyond
How the periodic table was built — Döbereiner's triads, Newlands' octaves, Mendeleev's bold predictions, Moseley's atomic numbers, and Seaborg's actinides — and why Mendeleev gets the credit.
The Island of Stability: Could Superheavy Elements Last Longer?
What the island of stability is, how magic numbers of protons and neutrons make some nuclei extra stable, the evidence from superheavy elements so far, and why reaching the island is so hard.
Oxidation and Reduction (Redox) Reactions Explained
What oxidation and reduction really mean, how to spot a redox reaction with oxidation numbers, oxidizing vs. reducing agents, and redox reactions you see every day.
Common Polyatomic Ions: List, Charges and How to Remember Them
A complete list of the polyatomic ions students need, with formulas and charges, the -ate/-ite and per-/hypo- naming patterns that make them easy to remember, and how to use them in formulas.
Why Is the Periodic Table Shaped Like That?
Why periods have 2, 8, 18 and 32 elements, why there's a gap at the top, why two rows float at the bottom, and the alternative designs — long-form, spiral and 3D — that chemists have proposed.
Hydrates Explained: Water of Crystallization and How to Calculate It
What hydrates are, how to read formulas like CuSO₄·5H₂O, how to calculate their molar mass and percent water, and how to find the formula of an unknown hydrate by heating.
Rare Earth Elements: What They Are and Why the World Needs Them
The 17 rare earth elements — the lanthanides plus scandium and yttrium — why they aren't really rare, why they're so hard to separate, and their role in magnets, electronics and clean energy.
What Is the Lightest Element? Hydrogen and the Runners-Up
Why hydrogen is the lightest element by every measure, the lightest elements ranked by atomic mass and density, the lightest metal and solid, and why 'lightest' can mean different things.